[netflow-tools] Latest format update diff

[Damien Miller]

oh, one more thing: please rotate your existing flowd logfile out of the
way before running an snapshot or this patch.

There are no checks (yet) against appending new-format records to an
old-format logfile so you will end up with a messed up log. If you make
this mistake, it is possible to recover using the Unix hexdump(1) and
split(1) utilities (and some patience), but it is best not to make the
mistake in the first place :)

-d